Who is Shmulek Nichtigal from The Cage and what is their importance?

Shmulek Nichtigal was the man who was taken away to a Nazi prison camp and then released by mistake. He came first to Riva but she didn't allow him to spend nights with them for fear that people would talk. He went to stay with Riva's friend, Henry, though there was a frantic search for him over the days after his release.